LTSpice, Reading values from plot

Discussion in 'Homework Help' started by SpiderRico, Mar 8, 2014.

  1. SpiderRico

    Thread Starter New Member

    Mar 8, 2014
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    0
    Hello all,

    When I run a simulation on LTSpice it generates a graph. By doing File->Export I can get the numerical values in a text file. However this doesn't help me much.

    For example I want to find the crossing point of Vout and Vin. I see they cross at some point in graph but can't tell exact value by looking at it. Is there a way for me to print that value ?
     
  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,500
    380
    hi,
    After you have plotted the graphs, place your cursor on the crossing point on the graph.

    Look at the bottom left of the LTS window at the Status bar, it will display the values under the cursor pointer as you move the cursor.

    E

    Post your *.asc file and I will explain further.
     
  3. crutschow

    Expert

    Mar 14, 2008
    12,991
    3,227
    After you have plotted the waveform you can also click on the waveform node-title at the top of the graph to generate a cursor that you can move along the graph. If you double-click then you will get two cursors which will give the absolute value at each cursor position and the difference between the two cursor positions.
     
    billegge and RidaElChami like this.
  4. SpiderRico

    Thread Starter New Member

    Mar 8, 2014
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    Thank you for replies. Now I need to measure the propagation delay of a capacitor. Any tips ?
     
  5. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    This pdf may help.
    E
     
  6. SpiderRico

    Thread Starter New Member

    Mar 8, 2014
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    No I mean I know how to measure the delay by hand but I ask if there is a way for simulator to derive it or do I have to find the values from the simulator and then plug them in the formula and calculate by hand ?
     
  7. crutschow

    Expert

    Mar 14, 2008
    12,991
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    As I previously noted, if you double click on a waveform title you will get two cursors. Move each of the two cursors to the points you want to measure. The cursor box will then give you the time difference between the two cursors.
     
  8. LvW

    Active Member

    Jun 13, 2013
    674
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    Propagation delay?
    I suppose, you are referring to phase differences between voltage and current, correct?
     
  9. SpiderRico

    Thread Starter New Member

    Mar 8, 2014
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    Okay, perhaps my question wasn't clear. I've got 2 tasks and and I'll try describing them as clear as I can. Any help is much appreciated.

    In LTSPICE, I've built a pseudo-NMOS inverter.

    1) I've a initial guess for Wn value of NMOS. I start the simulation with this value however, I need to optimize it and get a more precise value.

    Basically, when Vol < x for some x, I need to find the minimum Wn value that satisfies this inequality.

    2)Initially, nothing is connected to the output of inverter. Then, I connect a capacitor after finding my Wn value. At this point I need to find LOW-to-HIGH delay of the inverter.
     
  10. SpiderRico

    Thread Starter New Member

    Mar 8, 2014
    6
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    I guess if I can set Wn as a parameter then I can just find its value in graph. I tried right-clicking my NMOS and writing {x} in box but it didn't work.
     
  11. SpiderRico

    Thread Starter New Member

    Mar 8, 2014
    6
    0
    Okay I got the second one. Still no idea about the first one though.
     
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